Note: Descriptions are shown in the official language in which they were submitted.
101520CA 02264954 1999-03-01DESCRIPTIONPROJECTION DISPLAY DEVICETechnical FieldThe present invention relates to a projection displaydevice in which a light beam emitted from a light source ismodulated by a light valve using a liquid crystal panel orthe like, and the modulated light beam is enlarged andprojected via a projection optical system.Background ArtA projection display device has been known in which alight beam emitted from an illumination optical system isconverted into a modulated beam corresponding to imageinformation by using a liquid crystal light valve, and themodulated beam is enlarged and projected onto a screen(projection plane) via a projection optical system. Fig. 6shows an optical system in such a projection display device.As this figure shows, a projection display device 1000comprises an illumination optical system 80 including alight source 81 and a uniform illumination optical system 82,a liquid crystal light valve 100A to be irradiated with101520CA 02264954 1999-03-01light by the illumination optical system 80, and aprojection optical system 60A for enlarging and projectingemergent light from the liquid crystal light valve 100A ontoï¬a screen 900.In the projection display device 1000 having such aconventional configuration, the fânumbers FL and F? of theillumination optical system 80 and the projection opticalsystem 60A are designed to be nearly equal to each other.In general, the projection optical system 60A isfrequently represented by a single lens element, as shown inFig. 6, whereas it is normally composed of a plurality oflens elements. This means that a plurality of lens elementscan be replaced by a single lens element having a functionequivalent to that of those lens elements. It is assumedthat the fânumber F? of the projection optical system refersto the fânumber of the single lens element thus replaced,that is to say, a value 1P/dp that is obtained by dividing afocal distance 1P of the single lens element by a diameter dpof the lens.Furthermore, it is assumed that the fânumber FL of theillumination optical system refers to the fânumber of a lenselement disposed on the most downstream side of the opticalpath, that is, closest to the liquid crystal light valve1015CA 02264954 2002-01-08100A, which is an object to be illuminated, among aplurality of lens elements included in the illuminationoptical system. When the lens element disposed on the mostdownstream side of the optical path is a lens array composedof a plurality of small lenses, as shown in Fig. 6, the f-number FL of the illumination optical system does not referto the f-number of each small lens, but to a value 1L/dLobtained by dividing a distance 1L from the lens array to anobject to be illuminated by the maximum diameter dn of thelens array (e.g., the diameter in the case of a circularlens array, the length of the diagonal line in the case of arectangular lens array).On the other hand, projection display devices haverecently been required to display high-definition images.In order to display a highâdefinition image, it is necessaryto increase the number of pixels in the liquid crystal lightvalve. In a liquid crystal light valve in which pixels arearranged in a matrix, the peripheries of the pixels areshielded from light by a light-shielding layer called ablack matrix. Therefore, as the number of pixels in theliquid crystal light valve increases, the region occupied bythe black matrix enlarges, and conversely, the area of pixelapertures decreases. That is to say, the amount of light101520CA 02264954 1999-03-01emitted from the liquid crystal light valve decreases as thedefinition of the liquid crystal light valve increases, andtherefore, a projection image produced by the projectiondisplay device becomes dark as the definition of an image tobe projected increases. 9In order to avoid such harmful effects, a liquidcrystal light valve has been proposed which is provided witha microlens array composed of a plurality of microlenses sothat light is efficiently guided to corresponding pixelapertures by the microlenses.While incident light can be efficiently guided to thepixel apertures in the liquid crystal light valve providedwith the microlens array, emergent light from the liquidcrystal light valve, however, is diffused by the lensingaction of the microlens array. For this reason, theinclination angle of emergent light from the liquid crystallight valve having microlenses is greater than that ofemergent light from a liquid crystal light valve that doesnot have microlenses.Therefore, if a liquid crystal light valve havingmicrolenses is incorporated in the conventional projectiondisplay device 1000 in which the f-numbers of theillumination optical system 80 and the projection optical101520CA 02264954 2002-01-08system 60A are designed to be nearly equal, there is a fearthat a part of emergent light from the liquid crystal lightvalve will not be drawn into the projection optical system60A. As a result, light utilization efficiency is lowered,and an image.projected on the screen becomes dark.Summary of the InventionIn view of the above-described problems, an object ofthe present invention is to provide a projection displaydevice having a light valve with microlenses incorporatedtherein, wherein a bright projection image can be obtainedby preventing light utilization efficiency from beingdeteriorated due to light diffusion by the microlenses.Disclosure of the InventionIn order to solve the above problems, the presentinvention provides a projection display device comprising alight valve for modulating a light beam emitted from anillumination optical system, the light valve includingpixels arranged in a matrix; a microlens array having aplurality of microlenses for collecting incident light tothe pixels; and a projection optical system for enlargingand projecting the light beam modulated by the light valve,wherein the fânumber of the projection optical system is25 less than the fânumber of the illumination optical system.101520CA 02264954 1999-03-01In the projection display device of the presentinvention, the fânumber of the projection optical system isset to be less than that of the illumination optical systemso that emergent light from the liquid crystal light valvediffused by the microlenses is efficiently drawn into theprojection optical system. For this reason, it is possibleto prevent light utilization efficiency from beingdeteriorated due to light diffusion by the microlenses, andto obtain a sufficient effect of forming the microlenses inthe liquid crystal light valve. That is to say, it ispossible to cause a large amount of light guided to pixelapertures by the microlenses to efficiently reach aprojection plane, and to obtain a bright projection image ina projection display device in which a liquid crystal lightvalve having microlenses is incorporated.In order to make almost all emergent light from theliquid crystal light valve, which is diffused by themicrolenses, to be drawn into the projection optical system,the fânumber FF of the projection optical system is set tosatisfy the following equation:F, s [tan {tanâ1(2xFM) + tan'1(2xFL) â 9o°}]/2101520253035CA 02264954 2002-01-08..'7_.where the Fânumbers of the projection optical system, theillumination optical system, and the microlenses are Fp, FMand FM, respectively.In a preferred embodiment, the illumination opticalsystem may include a light source, and a uniformillumination optical system for splitting a light beamemitted from the light source into a plurality of partialbeams, and superimposing the partial beams onto the lightvalve. The adoption of such an illumination optical systemmakes it possible to uniformly illuminate the liquid crystallight valve, and to thereby obtain a high-contrastprojection image.In a further preferred embodiment, the illuminationoptical system includes a light source, a first lens platehaving a plurality of rectangular lenses for splittingemergent light from the light source into a plurality ofintermediate beams, and a second lens plate having aplurality of rectangular lenses for superimposing onto thelight valve the plurality of intermediate beams split by thefirst lens plate. This makes it possible to uniformlyilluminate the liquid crystal light valve, and to obtain ahigh-contrast projection image.In this case, the plurality of rectangular lenses thatconstitute the second lens plate may be decentering lenses.This allows the plurality of intermediate beams to besuperimposed at a shorter distance.In yet a further preferred embodiment, the illuminationoptical system includes a light source, first and secondlens plates having a plurality of rectangular lenses forsplitting emergent light from the light source into aplurality of intermediate beams, and a superimposing lensfor superimposing onto the light valve the plurality ofintermediate beams split by the first and second lensplates. This makes it possible to uniformly illuminate theliquid crystal light valve, and to obtain a high~contrastprojection image. The superimposing lens allows theplurality of intermediate beams to be superimposed at a10CA 02264954 2002-01-08shorter distance.In yet a further preferred embodiment, the illuminationoptical system may include a light source, and a light-collecting lens for collecting emergent light from the lightsource. When such an illumination optical system isadopted, since diffusion of light from the light source canbe prevented by a light collecting function of the light-collecting lens, light utilization efficiency is improved,and a bright projection image can be obtained.The projection display device may include a colorseparation optical system for separating a light beamemitted from the illumination optical system into aplurality of color beams, a plurality of aboveâdescribed101520CA 02264954 1999-03-01light valves for modulating the color beams separated by thecolor separation optical system, a color synthesizingoptical system for synthesizing the color beams modulated bythe light valves, and the projection optical system forenlarging and projecting the beams synthesized by the colorsynthesizing optical system.Brief Description of the DrawingsFig. 1 is a schematic structural view of an opticalsystem in a projection display device to which the presentinvention is applied.Fig. 2 is a schematic structural View of an equivalentoptical system for a red light beam.Fig. 3 is a View explaining the f-number of aprojection optical system.Fig. 4(a), Fig. 4(b), Fig. 5(a), and Fig. 5(b) areviews showing modifications of an illumination opticalsystem.Fig. 6 is a schematic structural view of an opticalsystem in a conventional projection display device.Best Mode for Carrying Out the InventionA projection display device to which the presentCA 02264954 2002-01-08-10-invention is applied will be described below with referenceto the drawings. In the description of the optical system,for convenience, three orthogonal directions are designatedX, Y, and Z, and Z indicates the direction of travel of5 light. The projection display device of this embodiment isof a type that separates a light beam emitted from anillumination optical system into three color beams of red,green, and blue, modulates these color beams through liquidcrystal light valves according to image information,10 synthesizes the modulated color beams, and enlarges andprojects the synthesized beams onto a screen via aprojection optical system.A. Configuration of the DeviceFig. 1 schematically shows the configuration of an15 optical system incorporated in a projection display device 1of this embodiment. The optical system in the projectiondisplay device*1 of this embodiment comprises anillumination optical system 80 having a light source 81, acolor separation optical system 924 for separating a lightï¬) beam W emitted.from the illumination optical system 80 intoa red beam R, a green beam G, and a blue beam B, threeliquid crystal light valves 100R, 100G, and 100B formodulating the color beams R, G, and B, a dichroic prism 10101520CA 02264954 1999-03-01_ 11 _serving as a color synthesizing system for synthesizing themodulated color beams, a projection optical system 60 forenlarging and projecting the synthesized beams onto thesurface of a screen 900, and a light guide system 927 forguiding the blue beam B of the color beams R, G, and B tothe corresponding liquid crystal light valve 100B.The illumination optical system 80 comprises the lightsource 81, and a uniform illumination optical system 82 forsplitting a light beam from the light source 81 into aplurality of partial beams, and superimposing those partialbeams onto the liquid crystal light valves 100R, 100G, and100B.The light source 81 includes a lightâsource lamp 811,such as a halogen lamp, a metal halide lamp, or a xenon lamp,and a reflector 812 for emitting emergent light from thelightâsource lamp 811 as nearly parallel light. As thereflector 812, a reflector having a reflecting surface,whose shape is parabolic, elliptic, or the like, is used.The uniform illumination optical system 82 includes afirst lens plate 821 and a second lens plate 822 that have aplurality of rectangular lenses. The uniform illuminationoptical system 82 also includes a reflecting mirror 823 soas to perpendicularly bend an optical axis 1a of emergent101520CA 02264954 1999-03-01light from the first lens plate 821 toward the front of thedevice. The first and second lens plates 821 and 822 arearranged so as to be at right angles to each other acrossthe reflecting mirror 823.Emergent light from the light source 81 is split into aplurality of intermediate beams by the rectangular lensesthat constitute the first lens plate 821, and superimposedonto the liquid crystal light valves 100R, 100G, and 100Bvia the rectangular lenses that constitute the second lensplate 822. In this way, since the liquid crystal lightvalves 100R, 100G, and 100B are illuminated using theuniform illumination optical system 82 in the projectiondisplay device 1 of this embodiment, they can be irradiatedwith uniform illumination light, which is effective inobtaining a highâcontrast projection image.The color separation optical system 924 includes a blueand green reflecting dichroic mirror 941, a green reflectingdichroic mirror 942, and a reflecting mirror 943. First, ablue beam B and a green beam G contained in a light beam Ware reflected nearly perpendicularly by the blue and greenreflecting dichroic mirror 941, and travel toward the greenreflecting dichroic mirror 942.A red beam R passes through this blue and green101520CA 02264954 1999-03-01-13..reflecting dichroic mirror 941, is reflected nearlyperpendicularly by the reflecting mirror 943 disposed behind,and is emitted from an emergent portion 944 for the red beamR toward the dichroic prism 10. Next, only the green beam Gof the blue and green beams B and G, which have beenreflected by the blue and green reflecting dichroic mirror941, is reflected nearly perpendicularly by the greenreflecting dichroic mirror 942, and is emitted from anemergent portion 945 for the green beam G toward thedichroic prism 10. The blue beam B passed through the greenreflecting dichroic mirror 942 is emitted from an emergentportion 946 for the blue beam B toward the light guidesystem 927. In this embodiment, the distances from anemergent portion of the illumination optical system 80 forthe light beam W to the emergent portions 944, 945, and 946of the color separation optical system 924 for the colorbeams are set to be substantially equal.On the emergent sides of the emergent portions 944 and945 of the color separation optical system 924 for the redbeam R and the green beam G, lightâcollecting lenses 951 andthe red beam R952 are disposed, respectively. Therefore,and the green beam G emerging from the emergent portions 944and 945 enter these lightâcollecting lenses 951 and 952,101520CA 02264954 2002-01-08-14..where they are collimated.The red beam R and the green beam G thus collimatedenter the liquid crystal light valves 100R and 100G, wherethey are modulated and given corresponding image information.That is to say, these liquid crystal light valves aresubjected to switching control by a driving means, which isnot shown, according to image information, and thereby, thecolor beams passing therethrough are modulated. As such adriving means, a known means can be used unaltered. Incontrast, the blue beam B is guided to the correspondingliquid crystal light valve 100B via the light guide system927, where it is similarly modulated according to imageinformation.The light guide system 927 comprises a lightâcollectinglens 954 disposed on the emergent side of the emergentportion 946 for the blue beam B, an incident-side reflectingmirror 971, an emergent-side reflecting mirror 972, anintermediate lens 973 interposed between these reflectingmirrors, and a lightâcollecting lens 953 disposed in frontof the liquid crystal light valve 100B. The blue beam B hasthe longest one of the optical path lengths of the colorbeams, that is, the distances from the light source 81 tothe liquid crystal light valves. Therefore, this light beam101520CA 02264954 1999-03-01_ 15 _undergoes the largest light loss. The light loss can,however, be reduced by interposing the light guide system-927.The color beams R, G, and B modulated through theand 100B enter theliquid crystal light valves 100R, 100G,dichroic prism 10, where they are synthesized. In thedichroic prism 10, dichroic layers are formed in the shapeof an X along bonded surfaces between four rightâangleprisms. A color image synthesized by the dichroic prism 10is enlarged and projected onto the surface of the screen 900at a predetermined position via the projection opticalsystem 60 that is a constituent of a projection lens unit.As the projection optical system 60, a telecentric lens maybe used.Next, a description will be given of the relationshipbetween the fânumber of the illumination optical system 80and the fânumber of the projection optical system 60.Although the optical paths leading from the illuminationoptical system 80 to the screen 900 via the liquid crystallight valves 100R, 100G, and 100B and the projection opticalsystem 60 are bent in order to contain the optical system ina compact space and for other reasons, they are, in opticalterms, practically equivalent to those of an optical system101520CA 02264954 1999-03-01-16-in which lenses are linearly arranged along the lightâsourceoptical axis. Fig. 2 shows an equivalent optical system fora red beam, from which the color separation optical system925, the light-collecting lens 951, and the dichroic prism10 described above are left out. Furthermore, equivalentoptical systems for a green beam and a blue beam are similar,and therefore, descriptions thereof are omitted.As shown in Fig. 2, the liquid crystal light valve 100Ris provided, on its light incident side, with a microlensarray 102 composed of a plurality of microlenses 101 inorder to prevent light utilization efficiency from beingdeteriorated due to the increase in definition. Themicrolenses 101 are formed corresponding to pixel apertures,and given optical properties such as to collect lightincident on the liquid crystal light valve 100R to thecorresponding pixel apertures.Therefore, in the projection display device 1 of thisembodiment, emergent light from the liquid crystal lightvalve 100R is diffused by the action of the microlenses 101,as shown by solid lines in Fig. 2. For this reason, theemergent light from the liquid crystal light valve 100Rspreads wider than emergent light (shown by broken lines inFig. 2) from a liquid crystal light valve in a projection101520CA 02264954 1999-03-01_ 17 _display device having a conventional configuration.In the projection display device 1 of this embodiment,the f-number F? of the projection optical system 60 is set tobe less than the f-number FL of the illumination opticalsystem so that emergent light from the liquid crystal lightvalve 100R, which is diffused by the microlenses 101, isefficiently drawn into the projection optical system 60.Although the projection optical system 60A is, ingeneral, frequently represented by a single lens element inmost cases, as shown in Fig. 2, it is composed of aplurality of lens elements in normal cases. This means thata plurality of lens elements can be replaced by a singlelens element having a function equivalent to that of thoselens elements. It is assumed that the f-number F? of theprojection optical system refers to the f-number of thesingle lens element thus replaced, that is to say, a value1P/dp that is obtained by dividing a focal distance 1? of thesingle lens element by a diameter dp of the lens.Furthermore, the f-number FL of the illumination opticalsystem refers to the f-number of a lens element that isdisposed on the most downstream side of the optical path,that is, closest to the liquid crystal light valves 100R,100G, and 100B, among a plurality of lens elements included101520CA 02264954 1999-03-01_ 13 _in the illumination optical system. In the case in whichthe lens element disposed on the most downstream side of theoptical path is a lens array consisting of a plurality oflenses, as in this embodiment, the fânumber FL does notrefers to the fânumber of each lense, but to a value 1L/dLobtained by dividing a distance 1L from the lens array to anobject to be illuminated by the maximum diameter dL of thelens array (e.g., the diameter in the case of a circularlens array, the length of the diagonal line in the case of arectangular lens array). Therefore, in the case of theprojection display device 1 of this embodiment, the fânumberFL of the illumination optical system is the fânumber of thesecond lens plate 822, that is, a value 1L/dL obtained bydividing a distance 1L from the lens plate 822 to the liquidcrystal light valve 100R by the maximum diameter ¢;of thelens plate 822 (e.g., the diameter in the case of a circularlens plate, the length of the diagonal line in the case of arectangular lens plate).In the projection display device 1 using the dichroicprism 10 of this embodiment, a certain liquid crystal lightvalve 100B among the liquid crystal light valves 100R, 100G,and 100B, which are objects to be illuminated, is frequentlypositioned farther from the illumination optical system 80101520CA 02264954 1999-03-01....]_9..than the other liquid crystal light valves. It is assumed,in such a case, that the distance 1L from the lens array toan object to be illuminated means the distance to the objectto be illuminated, which is nearer positioned. Inparticular, when the light guide system 927 is used as inthis embodiment, the lightâcollecting lens 954, which isdisposed at nearly the same position as those of the liquidcrystal light valves 100R and 100G, may be regarded as anobject to be illuminated.The entire optical system for radiating light onto theliquid crystal light valves 100R, 100G, and 10GB serving asillumination areas, that is, the optical path to the liquidcrystal light valves 100R, 100G, and 100B, and the opticalsystem existing on the optical path can be called anillumination optical system in a broad sense. For example,the color separation optical system 924, the light guidesystem 927, the lightâcollecting lens 951 and 952, and thelike shown in Fig. 1 are included in the illuminationoptical system in a broad sense. The illumination opticalsystem 80 in a narrow sense, however, mainly serves toradiate light onto the liquid crystal light valves 100R,100G,and 10GB. The present invention covers such anillumination optical system 80 in a narrow sense.10520CA 02264954 2002-01-08-20-In order for almost all emergent light from the liquidcrystal light valve 100R, which has been diffused by the«microlenses 101, to be drawn into the projection opticalsystem 60, the f-number F, of the projection optical system60, the f-number FL of the illumination optical system, andthe f-number Fâ of the microlens 101 provided in the liquidcrystal light valve 100R have the following relationship inthis embodiment. The f-number F; of the microlens 101 refersto a value obtained by dividing the focal distance of eachmicrolens 101 by the diameter thereof.Fig. 3 shows the relationship among the f-numbers ofthe illumination optical system 80, the projection opticalsystem 60, and the microlens 101. As this figure shows, abeam angle 9, of the illumination optical system 80 and abeam angle 0, of the microlens 101 are obtained from thefollowing equations (1) and (2):6, 90° â tanâ(2 x FL) .â (1)9, 90°- tan*(2 x F") .â (2)A light beam guided to the projection optical system 60is a diffused beam from the illumination optical system 80that is also diffused by the microlens 101. For this reason,101520CA 02264954 2002-01-08-21-an angle 0, of the light beam guided to the projectionoptical system 60 is the sum of the beam angle &âof theillumination optical system 80 and the beam angle Q,of themicrolens 101, and is obtained from the following equation6,.=6,_+8,,180° â tan"(2xF,_) â tan"(2xF,,) (3)In this embodiment, the fânumber of the projectionoptical system 60 is set to satisfy the equation (4) byincreasing the entrance pupil of the projection opticalsystem 60 so that all light beams having the angle 6, aredrawn into the projection optical system 60.F, s {tan(9o°âe,,)}/2 (4)That is to say, according to the equations (3) and (4),the f-number F, of the projection optical system, the f-number F, of the illumination optical system, and the f-number PM of the microlens in the projection display.deviceof this embodiment, are set to satisfy the equation (5):101520CA 02264954 1999-03-01_ 22 _F1, 5 [tan {tan'1(2xFM) + tanâ1(2xFL) â 9o°}]/2 (5)Therefore, for example, when the fânumber FL of theillumination optical system 80 is 2.5 and the fânumber FM ofthe microlens 101 is 3.5, the fânumber F? of the projectionoptical system 60 is set to be less than approximately 1.4.when the fânumber FL of the illumination optical system 80 is5.0 and the fânumber Fâ of the microlens 101 is 3.5, the f-number F? of the projection optical system 60 is set to beless than approximately 2ØIn this way, the fânumber FP of the projection opticalsystem 60 is specified in the projection display device 1 ofthis embodiment so that emergent light from the liquidcrystal light valves 100R, 100G, and 100B diffused by themicrolenses 101 is efficiently drawn into the projectionoptical system. For this reason, it is possible to avoid asituation in which a part of emergent light from the liquidcrystal light valves 100R, 100G, and 100B with microlensesmisses the projection optical system 60, and to therebyprevent light utilization efficiency from being lowered dueto diffusion by the microlenses 101. That is to say, it ispossible to cause a large amount of light guided to thepixel apertures by the microlenses 101 to efficiently reach101520CA 02264954 1999-03-01_ 23 _the projection plane, and to obtain a bright projectionimage in a projection display device that includes liquidâcrystal light valves having microlenses.B. Modifications of Illumination Optical SystemThe above-described illumination optical system 80 maybe replaced by illumination optical systems 80A to 80D shownin Fig. 4(a), Fig. 4(b), Fig. 5(a), and Fig. 5(b). In Figs.4(a) to 5(b), similar constituents to those in theillumination optical system 80 are given the same numerals,and a detailed description thereof is omitted.The illumination optical system 80A shown in Fig. 4(a)comprises a uniform illumination optical system 82Aincluding two lens plates 821 and 822 and a superimposinglens 824, and a light source 81. While intermediate beamssplit by the first lens plate 821 are superimposed on theliquid crystal light valves 100R, 100G, and 100B by thesecond lens plate 822 in the above-described illuminationoptical system 80A, they are superimposed via thesuperimposing lens 824 in this modification. In thismodification, the fânumber FL of the illumination opticalsystem means the fânumber of the superimposing lens 824 thatis disposed on the most downstream side of the optical path.In the illumination optical system 80B shown in Fig.101520âCA 02264954 2002-01-084(b), a section constituted by the second lens plate 822 andthe superimposing lens 824 in Fig. 4(a) is replaced by asingle decentering lens plate 8228 having the same functionsas those of both the elements. In this modification, the f-number FL of the illumination optical system is representedby a value 1L/db obtained by dividing a distance 1L from thelens plate 822B, which is disposed on the most downstreamside of the optical path, to an object to be illuminated bythe maximum diameter ¢;of the lens plate 822B (e.g., thediameter in the case of a circular lens plate, the length ofthe diagonal line in the case of a rectangular lens plate).The illumination optical system 80C shown in Fig. 5(a)comprises a uniform illumination optical system 82Cincluding two lens plates 821C and 822C, and a light source 81C.The light source 81C includes a light-source lamp 811 and anelliptic reflector 812C. The light source 81C in thismodification emits convergent light, as distinct from theaboveâdescribed light source 81 that emits parallel light.The lens plates 821C and 822C that constitute the uniformillumination optical system 82C are shaped in accordancewith the width of convergent light emitted from the lightsource 81C.The functions of the lens plates 821C and 822Care similar to those of the lens plates 821 and 822 in the10520CA 02264954 2002-01-08- 25 -illumination optical system 80. In this modification, thef-number FL of the illumination optical system is representedby a value IL/d; obtained by dividing a distance 1L from thelens plate 822C, which is disposed on the most downstreamside of the optical path, to an object to be illuminated bythe maximum diameter dL of the lens plate 822C (e.g., thediameter in the case of a circular lens plate, the length ofthe diagonal line in the case of a rectangular lens plate).The illumination optical system 80D shown in Fig. 5(b)comprises a light source 81, and a light-collecting lens 825.The light-collecting lens 825 serves to prevent lightemitted from the light source 81 from diffusing. In thismodification, the fânumber FL of the illumination opticalsystem means the fânumber of the light-collecting lens 825that is disposed on the most downstream side of the opticalpath.C. other EmbodimentsWhile the above-described projection display device 1is a front projection display device that performsprojection from the side where a projection plane isobserved, the present invention may also be applied to arear projection display device that performs projection fromthe side opposite to the side where a projection plane isobserved.CA02264954 1999-03-01
